Multistage propeller fan



. Jan; 18, 1944.

H. F. HAGEN MULTISTAGE PROPELLER FANS Filed Jan. 26, 1942 2 Sheets-Sheet 1 m Z g E aan ssmzdg I ifi by (324,410. MT

Jan. 18, 1944. H.'F. HYIAGENY 2,339,602

'MULTISTAGE PROPELLER FANS Filed Jan. z, 1942 '2 Sheets-Sheet 2 filed November 14, 1940.

of a two stage. invention;

f two 2,339,602 MULTISTAGE PROPEILER FAN I g v F. Hagen, Wellesley, Mass, minor to 7 UNITE- STATES f ATE Harold g B. F. Sturtevant Company, Boston, Mass.

i i aucnisnum 26,1942, Serial No.4 28,211;' 1'- scmmc'xcLzso-mi i ht of the dips in the characteristic curves.

Thus in normal operation, no-now separation This invention relates in propeller tans and has as its object the elimination of fluctuations oi pressure-and volume caused by flow separation.

This application is a continuation-in-part oi my copending application,

The fluctuations o! pressure'and volume caused by flow separation are very objectionable and H are overcome in this invention by providing in a multi-stage propeller tan, propeller wheels which are so designed and proportioned with respect to each other and to the overall. performance desired, that the stalling point for the blades oi one wheel occurs at a diflerent point from that of another, and, that the overall characteristic curve is free from the dip or dips symbolical or flow separation.

In a preferred embodiment oi the invention as embodied in a two stage propeller fan, the propeller wheel of the first stage handles substantially 60% of the work and the propeller wheel of the second stage handles substantially 40% of the work. By way 01! example in a two stage propeller tan providing 40" pressure, the first I stage provides pressure and the second stage I provides 15" pressure.

Serial No. 365,598,-

me and tionable, theiincrease' in. the pressure causes'a further increase involunie'. The reflect is cumulative and troublesome pulsations are set up.

--Exper ience-has shown that where charac teristiccurves; have flat horizontal portions, the

The invention will-now be described with r rerenceto'thedrawingaoi which:

Fig. 1 is a graph showing the characteristics propeller fan embodying this Fig. 2 is a transversesection through the propeller fan, the characteristic curves of which are illustratedbyFigrh" Pig. 3 is a. transverse section through anotherstage propeller tan embodying this invention;

Fig. 4 is a transverse section through still another two stage propeller ian embodying this invention;

, Pig. 5 is a planview looking downwardly upon the propeller wheel or the first stage of Fig. 4,

Fig. 6-is a plan view looking downwardly upon the propeller wheel of the second stage of Fig. 4.

The propeller wheels A and B of a two stage propeller tan were designed to have the characteristic curves 0! Fig.1. The burble or stalling v point of thewheel A. is shown on its character- 1 istic curve by the'dip in the curve at C. The i fstalling point oi the wheel B is shown onits characteristic curve by the dip in the curve at n.

-- Propellefians of this typeare operated normally to provide pressures and corresponding volumes which occur, withrespect to Fig. 1, to the 55 fans 'aze'stablewhen throttled" through the flat portions 0 observable pulsations beingjset up. There is ,damping either positive or negative and the resistance of the system prevents pulsa- Hons. 1 v

The two wheels A and cc designedthat their overall characteristicciirv'e, the upper curve of Fig. 1, has noappreciiible. dips *0: peaks so that the two wheels-j. working, together operate without pulsations on :su'rges provide smooth performance. Thisflis accomplishedbyne'smnim the wheels so that and in which the second stage may be designed wheel and the second stage wheel difier in their blade areas; Except for this difference the blades may have the same design characteristics.

Referring now to Fig. 2, the two stage propeller ian there illustrated consists oi the casing 6, the first stage propeller wheel A, the second stagepropeller wheel B, the spin neutralizing vanes 8 between the wheels, the downstream spin neutralizing vanes 1 and the diflfuser 8. i In the embodiment illustrated, the wheel A may have 21 a'iO-mcci This-gum is in whet-{min v where the tei'istic curve of one wheel has a dip'as atjthe pointsilC or D 01 Fig. 1, the characteristic ofzthe other wheel has a rising, compensating characteristic.-. The propeller fan illustrated by Figs. 2- 6illu strate several different ways in whichathe first stage of a two stage propeller fan may be designed to handle substantially of the worli blades and the wheel B may have 23 blades. The vanes 8 may be 30 in number and the vanes I may be 27 in number.

7 wheel A is preferably about 60% of the total efiective blade area while the effective surface area '01 the blades of the wheel B is about 40% the total area. The difference in the blade area of of one wheel at one pressure and corresponding volume, resulting from the stalling point of that wheel, is compensated by a rise in the curve substantially diilerent pressures the pressurevolume characteristics of two of the wheels being such that the pressure irom one wheel rises suii'iciently at the stalling point of the other wheel to compensate for the fall in pressure at d the said stalling point of said other wheel.

the two wheels results from the difierence in the number of blades -and in the diflerence'in blade lengths of the wheels. Wheel B has a hub 9 whichis larger than the hub ill of the wheel A so that the blades of wheel A pr'ovide most of the total blade area due both to their greater number and to their greater length.

In the embodiment of the invention illustrated by Fig. 3, thehubs 9 and ill have the same diameter and the reduction in the length of the blades oi! the wheel B is obtained through converging the casing 5 to form an air passage in the vicinity of and to the rear of the wheel B, which is smaller than the air passage containing the wheel A. The reduction in the blade area of the wheel B may be obtained wholly through reducing the length of the blades thereof or through the reduction in the length of. the blades of the wheel B; and their number.

3. A multi-stage propeller fan having two dissimilar propeller wheels, said wheels being so constructed and arranged that they provide substantially different pressures at the designed volume, and that they have stalling points at substantially different pressures with such pressure-volume characteristics that the pressure from one wheel rises sufficiently at the stalling point of the other wheelto compensate tor the fallin pressure at the said stalling point oi said otherwheel.

4. A multi-stage propeller fan having two dissimilar propeller wheels, said wheels having substantially diii'erent blade areas whereby one wheel provides a substantially greater pressure at the designed volume than the other wheel, said wheels being so constructed and arranged Y that they hav stalling points at substantially different pressures with such pressure-volume characteristics that the pressure from one wheel rises sufllciently at the stalling point 01 the In the embodiment of theinvention illustrated by Figs. 4, 5 and 6, the blades oi wheels A and B have the same length, the reduced'blade area of the bladesoi the wheel B being obtained by a reduction in the number of its blades. Thus as illustrated by Fig. 5, the wheel A'may have 12 blades, and as illustrated by Fig. 6, the wheel B may have 8- blades. The design characteristicsof all blades .thus may be the same so thatthe wheel A has 60% of the total blade area and sothat the wheel B has 40% of the total blade 7 area, through proportioning the number of blades. Thewheels A and B of Figs. M have been illustrated as having relatively small number of blades for ease oiillustration. The characteristics of these wheels follow substantially, however, the curves shown by Fig. l.

While the invention has been designed as embodied in a two stage propeller fan, it could be embodied in any multi-stage propeller fan and the principle involved 0! adding'individual characteristics to secure a combined desired characteristic may be secured by adding two characteristics as described herein or any number more than two. In the claims, the term multistage" may refer to a two stage fan or to two stages of a fan having three or more stages.

While embodiments of the invention have been disclosed forthepurpose of illustration, it should be understood that theinvention is not limited to the precise disclosureas other embodiments of the invention may be suggested by those skilled in the art without departure from the essence of the invention.

What is claimed is: I

1. A multi-stage propeller fan with dissimilar propeller wheels, said wheels having different other wheel to compensate for the fall in pressure at the said stalling point of said other wheel. I

5. A multi-stage propeller fan having two dissimilar propeller wheels, the blades or one of said wheels being substantially longer than the blades of the other ofsaid wheels whereby one wheel provides a substantially greater pressure at the designed volume than the other wheel, said wheels being so constructed and arranged that theyhave stalling points at substantially different pressures with such pressure-volume characteristics that the pressur'e'from one wheel rises sufiiciently at the stalling point of the other wheel to compensate for the fall in pressure at the said stalling point of said other wheel.

6. A multi-stage propeller fan having two dissimilar propeller wheels, the blades of one of said wheels being substantially greater in number than the blades of 'the other'ofsaid wheels whereby one wheel provides a substantially greater pressure at the designed volume than the other wheel, said wheels being so constructed and arranged that they have stalling points at substantially different pressureswith such pressure-volume characteristics that the pressure from one wheel rises suificiently at the stalling point of theother wheel to compensate for the fall in pressure at the said stalling point of said other wheel. a V

1 7. A multi-stage propeller fan having two dissimilar propeller wheels, the blades of one of said wheels being greater in number and longer than the blades of the other of said wheels whereby one wheel provides a substantially greater pressure at the designed volume than the other wheel, said wheels being so constructed and arranged that they have stalling points at substantially diiferent pressures with such pressure-volume characteristics that the pressure from one wheel rises sufliciently at the stalling 3/2 the pressure provided by the other wheel of a 3 said pair at the designed uolume, and that the two wheels have'stallin: points at substantially diil'erent pressures with such pressure-volume characteristics that the pressure from one wheel rises sumciently at the stalling point at the other wheel tocOmPenate for the fall in pressure at the said stalling point of said other wheel.

HAROLD I". HAGEN. 

